Could it be? What are the chances?

Currently going on CD 40. Have been cramping a lot lately, boobs feel tingly/burning/sore, experiencing extreme fatigue, but keep getting BFN. The last frer I took was 2 days ago and was negative. I have somewhat irregular cycles and have no idea for sure when I ovulated (going to start temping this next cycle if it comes). Well I thought I was out...but today I experienced spotting! It was like brown CM only when I wiped...Has anyone ever had this happen and actually ended up preggers?